Top trade officials of 12 Pacific Rim nations continued haggling over rules for trade in drugs, cars and dairy products this week as they try to work out the final details of a complex deal that could cover about 40 percent of the global economy.

The United States, Japan, Canada, Vietnam and eight other nations have been working on the proposed Trans-Pacific Partnership for years, and they were hoping to wrap up an agreement during this week's negotiations in Atlanta.

The discussions were slated to end earlier this week, but correspondent Doug Palmer of Politico said no agreement had been announced by early Saturday evening.

The issues include Washington's push to extend patent protection on a promising new class of drugs for longer than other nations want. Other disputes include dairy exporter New Zealand's push for greater access to Canada's dairy market, and squabbles between the United States and Japan over auto industry trade.

TPP supporters say the pact would boost trade and economic growth for participants. U.S. critics of the deal say it would do too little to protect American jobs or the environment. They also contend that it would raise the cost of some drugs.

Resolving these and other disputes has been made more difficult by pending elections in several key nations, where some workers and farmers worry that increased trade will mean decreased employment. Many businesses support expanded trade as a way to open new markets to exports.

The 12 nations working on the TPP are United States, Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore and Vietnam.